In recent years, semiconductor substrates are conventionally separated from a silicon wafer or the like by using a diamond blade. The separation method of the substrate suffers from problems such as a loss of cutting portion, that is, a blade width lost in the course of cutting, and a chipping of the substrate that deteriorates a yield rate of the substrate.
A method to cope with the above-described problems is disclosed in Japanese Patent Document JP-3408805 as shown in FIGS. 4A to 4C. In this method, a laser light is used to form a modified area in the semiconductor substrate by multiphoton absorption with a focused beam to a specific depth of the substrate. The modified layer in the substrate is used as a starting point of dicing. The dicing and separation of the substrate are explained in sequence in the figure.
As shown in FIG. 4A, a reverse side of a semiconductor substrate 1 (a surface that does not have an element formed thereon) has a Die Attach Film 2 (DAF: a film type adhesive) for implementing a semiconductor chip 1e that is separated from a wafer. An opposite side of the substrate 1 to the reverse side has a dicing film 5 (also known as a dicing sheet, or a dicing tape) for holding the chip 1e after separation by dicing. The DAF 2 and the dicing film 5 are, for example, made from a synthetic resin film with an adhesive pasted thereon.
A laser beam 4 is irradiated with a focus point P in a lower portion of the substrate 1 to trace a dicing line L1 from outside of the substrate 1 in a process of pre-dicing step. In this manner, a modified area 1c is formed in the substrate 1 as a collective form of cracks around the focus point P where thermal strain by concentration of the laser beam 4 is induced. Then, the depth of the focus point P is changed to form another modified area 1c that traces the dicing line L1. As a result, at least one layer of modified area 1c is formed in the substrate 1. Each of the dicing lines L1 is traced by the modified area 1c in this manner as shown in FIG. 4A. Then, the dicing film 5 is pulled toward both sides in directions indicated by arrows F2 and F3 in FIG. 4B to form a cut 1b in the modified area 1c along the dicing line L1 in the substrate 1c as a result of expansion of the crack with an application of shearing force. Then, a portion between the cuts 1b, 1b is moved by a pressing member 6 in an upper direction (shown as an arrow F4 in the figure) from the reverse side of the substrate 1 to remove the semiconductor chip 1e by tearing off the DAF 2 (FIG. 4C).
However, a conventional method of shearing leaves the DAF 2 in an irregular shape, that is, an actual tearing off line goes away from an intended line L1. In this case, the strength of implementation will decrease because of an insufficient space of adhesion when the DAF 2b has a size that is smaller than a standard size. In addition, the implementation will be defective when a residue DAF 2c extending from the semiconductor chip 1e (shown in FIG. 4C) prevents a normal implementation. The semiconductor chip 1e suffers from a same type of problem when the implementation of the chip 1e by soldering with a metal foil is substituted for the implementation by using the DAF. That is, it is problematic in the implementation of the semiconductor chip when the DAF or the metal foil is not suitably cut with the semiconductor chip.